I think you're viewing this from a narrow perspective. Not everyone will be part of a pre-organized squad/platoon.

If you're a random player in a random squad, why should you be the AV guy (and possibly be gimped during most of the fight)? Who decides that, and who exactly is to blame when MAXes steamroll through your group? Was everyone stupid? Would everyone be stupid if too many people chose an AV class that is less effective against regular infantry? Should randoms be punished because they play the game on a different level? I don't think so.

Hopefully MAXes won't be near-impervious to small arms fire. If they are, they would be the only infantry class that needs a direct counter, and that would just be wrong.

Don't take this the wrong way, but from my point of view, it looks like you are viewing it from a narrow perspective. Planetside isn't about 1 squad versus another, it's about squads upon squads of people all battling each other. So across that many people, you will see different "classes". It happens naturally just as it does in Planetside.

So for example, if you are defending a base, you see a Commander shout out, "Incoming Max Crash" well a certain number of people will switch to their loadout to counter the Maxes. Obviously not everyone will run and grab a deci, but if enough people do, the MCT fails, if enough people don't the MCT will crush. Not everything has to be totally organized to still work, in fact the chaos is part of the fun.